The present invention relates to a new class of chromogenic thiol indicators based on the benzoisothiazolone ring system. These indicators can be used in the detection of thiol groups produced by chemical or enzymatic reactions.
Classically, a number of color producing disulfides have been used for the detection of thiol residues. The most frequently used compound is the Ellman's reagent, 5,5'-dithio(2-nitrobenzoic acid), which in the presence of thiols produces the yellow color of p-nitrothiophenol at 405 nm (nanometers).
Other commonly used reagents for the detection of thiols include the 2,2'- and 4,4'-dipyridyl disulfides, whose reduced chromophore has an absorption at 340 nm.
There have been several attempts in the literature to prepare disulfide reagents which produce colors of longer wavelength and extinction. These compounds are of particular value in the development of diagnostic test systems because more highly colored substances can be more easily read in the presence of a number of colored interfering substances in urine, serum, and whole blood. None of these compounds (see the literature section) to date has found use in diagnostic application. This is largely because of a combination of factors, such as low reactivity with thiols due to their poor solubility or the poor chromogenic properties of the resulting reduced dyes in aqueous soluents.